Process of producing all skin rayon



PROCESS OF PRODUCING ALL SKIN RAYON Harry H. Hall, Springfield, Pal, assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Original application Dec. 36, 1954, Ser. No. 478,913, now Patent No. 2,895,737, dated July 21, 1959. Divided and this application Nov. 21, 1958, Ser. No. 775,357

9 Claims. (Cl. 106-165) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthat'e is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is sub-- sequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its propertiessuch as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a coreportion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structureand these different portions possess diiierent swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and creuulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff.

it has now been discovered that the presence of small amounts of alkali-soluble phosphoric acid esters of alkylene oxide adducts of fatty alcohols in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, fihns, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the alkylene oxide adduct is maintained with certain limits and the composition of the spinning bath is maintained within certain f nited States Patent ICE composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

The fatty alkyl group or radical is a straight chain monohydric alcohol containing from 6 to 24 carbon atoms and may be saturated or unsaturated. The radical may be obtained from the fatty acids derived from animal and vegetable fats and oils such as coconut oil, cottonseed oil, corn oil, soya bean oil, palm oils, peanut oil, tallo-w and the like andthe hydrogenated fats and oils. The term fatty alcohol is used herein to designate these straight chain monohydric, primary alcohols or higher primary aliphatic alcohols and includes such alcohols whether prepared from fats and oils or from other sources. The fatty alcohol employed in preparing the substances as utilized for the purposes of this invention may be a pure compound wherein a relatively pure fatty alkyl radical, such as a lauryl or oleyl radical, is employed in preparing the adduct, or the fatty alcohol may consist of a mixture of alcohols where the fatty alkyl radicals are obtained from a mixture of fatty acids of a particular fat or oil such as coconut oil.

The adducts, or as more technically classed, the polyoxyalkylene glycol ethers, may be prepared by reacting a fatty alcohol, or a mixture of fatty alcohols with an alkylene oxide or. a polyoxyalkylene glycol. Adducts or ethers which are satisfactory for the purposes of this invention may be derived from capryl, lauryl, myristyl, oleyl, stearyl and the like alcohols or from a mixture of fatty alcohols such as derived from the fatty acids of coconut oil or other fat or oil.

The alkylene oxide adducts or polyoxyalkylene glycol ethers of the fatty alcohols may have at least about 2 to about 20 or more alkylene oxide units per molecule, preferably between about 4 and 10 alkylene oxide units per molecule of the fatty alcohol. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and in alkali solutions, the ethylene oxide adducts or polyoxyethylene glycol ethers are preferred. For purposes of illustration only, the invention is described by reference to the ethylene oxide adducts but it is to be understood that other alkylene oxide adducts such as propylene oxide adducts are equally satisfactory.

The modifiers employed in the present invention may be any of the phosphoric acid esters, namely, the mono-, di-, or tri-esters, with the polyoxyalkylene glycol ethers of the fatty alcohols. In accordance with conventional practice, the term phosphoric acid is used to designate the ortho form or modification of the acid. The mono-, diand tri-esters designate compounds in which 1, 2, and 3 hydroxyl groups of the acid have been esterified with the polyoxyalkylene glycol ethers of the fatty alcohol. In the monoand di-esters, the remaining active hydrogen atoms of the acid may be replaced with an alkali metal such as sodium, potassium and the like. Thus, the invention contemplates the use of mono-, di-, and tri-esters of the alkylene oxide adduct of the fatty alcohol with phosphoric acid and monoand di-esters of the alkylene oxide adduct of the fatty alcohol with diand mono-alkali metal salts of phosphoric acid, respectively.

The various esters of the ethers or alkylene'oxide adducts are satisfactory providing they possess the required solubility.- That. is, the adduct must have sufiicient solubility to permit a minimum amount of the ester to be dissolved in the viscose.

The amount of the ester or modifier which is incorporated in the viscose must be at least about 0.25% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from 0.5% to 2.5%. Lesser amounts do not result in the producamazes tion of products consisting entirely of skin and greater amounts afiect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The ester may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanth-ated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The ester is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of a phosphoric acid ester may have a salt test above about 7 and preferably above about 8 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the ester in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath containing from about to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. ther metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C. preferably between about 45 C. and about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufiiciently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% celluose, 6% caustic-viscose and containing the phosphoric acid esters lies between about 5% and about 8%. The acid concentration may be increased as the amount'of the 4 ester is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of ester and the concentration of caustic in the viscose. 1A1]. skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the ester is increased beyond about 4% while other conditions are maintained constant. Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 41% (based on the weight of cellulose) carbon disulfide, and 1% (based on the weight of cellulose) of a di-ester of phosphoric acid and an ethylene oxide ether of lauryl alcohol, the ether containing 4 ethylene oxide units per molecule, and having a salt test of about 8 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 8% results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the production of products having shin and core. A lowering of the amount of the ester, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. it has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about 8.5%.

The presence of the ester in the viscose retards the coagulation and, therefore, the amount of ester employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the other is employed in. amounts within the lower portion of the range, for example, about 0.6% to 0.75%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period suflicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In general, a closer control of the spinning conditions must be maintained in order to produce all skin products of relatively large cross-section such as filaments above about 6 to 8 denier. It has been discovered that by the use of the esters as described herein, all skin products of relatively large cross-section such as filaments above about 6 to 8 denier may be readily produced without maintaining the close control and that as the cross-section is decreased, a closer control of the spinning conditions must be maintained.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and maybe stretched from about 70% to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and'other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of. zinc sulfate if regeneration has not previously been completed.

The treatment following the final' regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the phosphoric acid esters and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the phosphoric acid esters have superior abrasion and fatigue resistance characteristics and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, carpet and rug fibers or yarns and the like, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7% cellulose, about 6.5% caustic soda, and having a total carbon disulfide content of about 35% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5% carbon disulfide was then added to the mixer and the mass mixed for about one hour. The desired amount of a phosphoric acid ester of an ethylene oxide adduct of a fatty alcohol was added to the solution and mixed for about /2 hour. The viscose was then allowed to ripen for about 30 hours at 18 C.

Example 1 Approximately 1% (based on the weight of the cellulose) of a phosphoric acid ester was added to and incorporated in the viscose as described above. The additive or modifier was a tri-ester of phosphoric acid and an ethylene oxide adduct of oleyl alcohol containing about 4 ethylene oxide units per molecule of oleyl alcohol. The viscose employed in the spinning of filaments had a salt test of 8.5 and was extruded through a spinneret to form a 340 denier, 40 filament yarn at a rate of about 25 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.3% sulfuric acid, 8.7% zinc sulfate and 19% sodium sulfate. The yarn was passed over a godet from which it was conducted to thread-advancing reels where it was stretched about 57%, washed free of acids and salts with hot water (98 C.), dried and collected on The individual filaments have'a smooth, non-creme" lated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. 1500 The filaments of a control yarn spun with the same vis-' cose but without the addition of the phosphoric acid ester and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about I skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 344 denier, 40 filament yarn by extrusion into a spinningbath containing 7.4% sulfuric acid, 8.7% zinc sulfate and 19% sodium sulfate. The bath was maintained at 60 C., and the extrusion rate was about 25 meters per minute. The filaments were subsequently passed over a godet from which they were conducted to thread-advancing reels and stretched about 57%, washed free of acids and salts with hot water (98 C.), dried and collected on cones.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirety of skin while the control filaments have a very irregular and serrated surface and consist of about 65 skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 1% of a tri-ester of phosphoric acid and an ethylene oxide adduct of lauryl alcohol containing 4 ethylene oxide units per molecule of lauryl alcohol. The viscose had a salt test of 9.0 and was spun into a 316 denier, 40 filament yarn by extrusion into a bath containing 7.8% sulfuric acid, 8.6% zinc sulfate and 19% sodium sulfate. The bath Was maintained at a temperature of 60 C. The extrusion rate was about 25 meters per minute. The yarn was passed over a godet from which it was conducted to thread-advancing reels Where it was stretched about 57%, washed free of acid and salts with hot water (98 C.), dried and collected on cones.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no ester in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of. about 65% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples. a

' Example 4 T o a viscose solution as described above, there was added about 1% of a monosodium di-ester of phosphoric acid and an ethylene oxide adduct of lauryl alcohol containing about 4 ethylene oxide units per molecules of lauryl alcohol. The viscose had a salt test of 8.1 and was spun into a 336 denier, 40 filament yarn by extrusion into a bath containing 7.5% sulfuric acid, 8.1% zinc sulfate and 19% sodium sulfate. The bath was maintained at a temperature ,of about 60 C. The extrusion rate was about 25 meters per minute. The yarn was passed over a godet from which it was conducted to thread-advancing reels where it was stretched about 57%, washed free of acid and salts with hot water (98 C.), driedand'collected on cones. I

The individual filaments were readily distinguishable actress from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin whereas control filaments have a very irregular and serrated surface and consist of about 65% skin and the balance core with a sharp line of demarkation between the skin and 1 Not determined.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance,'fiex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by con.- ventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The phosphoric acid esters may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts may be added at any desired stage in the production of the viscose and may be present in the cellulose raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

If desired, small amounts of the ester may be added to the spinning bath. Since the substances are also water-soluble, some of the ester will be leached from a the filaments and will be present in the bath.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2. hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and 90% dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a division of my copending application Serial No. 478,913, filed December 30, 1954, entitled Process of Producing All Skin Rayon, now Patent No. 2,895,787, dated July 21, 1959.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and his to be understood that changes and variations may be made Without departing from the spirit and scope of the invention as defined by the appended claims.

I claim: 7 v

1. A viscose spinning solution containing a small amount of a modifier selected from the group-consisting of alkali-soluble esters of phosphoric acid and of alkalisoluble esters of alkali-metal acid salts of phosphoric acid With polyoxyalkylene glycol mono-others of fatty alcohols and mixtures thereof, the mono-others containing at least 2 alkylene oxide units per mole of fatty alcohol, the fatty alcohols being selected from the group consisting of saturated and unsaturated straight chain monohydric alcohols containing from 6 to 24 carbon atoms, the alkylene oxide being selected from the group consisting of ethylene oxide and propylene oxide, said small amount of the modifier being a quantity sufiicient to impart a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the Viscose at a sodium chloride salt test of at least 7 into an aqueous bath containing from 15% to 22% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount exceeding the slubbing point but not exceeding 8.5%, but the quantity being insufficient to adversely affect the physical properties of such products.

2. A viscose spinning solution containing from about 0.25% to about 4%, based on the weight of the cellulose in the viscose, of a modifier selected from the group consisting of alkali-soluble esters of phosphoric acid and of alkali-soluble esters of alkali-metal acid salts of phosphoric acid with polyoxyalkylene glycol mono-others of fatty alcohols and mixtures thereof, the fatty alcohols being selected from the group consisting of saturated and unsaturated straight chain monohydric alcohols containing from 6 to 24 carbon atoms, the mono-others containing at least 2 alkylene oxide units per mole of fatty alcohol, the alkylene oxide being selected from the group consisting of ethylene oxide and propylene oxide.

3. A viscose spinning solution as defined in claim 2 wherein the modifier is an ester of phosphoric acid as defined in claim 2.

4. A viscose spinning solution as defined in claim 2 wherein the modifier is an ester of an alkali-metal acid salt of phosphoric acid as defined in claim 2.

5. A viscose spinning solution as defined in claim 2 wherein the modifier is an ester of a polyoxyethylene glycol mono-ether of a fatty alcohol as defined in claim 2.

6. A viscose spinning solution as defined in claim 2 wherein the modifier is a tri-ester of phosphoric acid with a polyoxyethylene glycol mono-ether of oleyl alcohol, the mono-ether containing from about 4 to 10 ethylene oxide units per mole of oleyl alcohol.

7. A viscose spinning solution as defined in claim 2 wherein the modifier is a monosodium di-ester of phosphoric acid with a polyoxyethylene glycol mono-ether of oleyl alcohol, the mono-ether containing from about 4 to 10 ethylene oxide units per mole ofoleyl alcohol.

8. A viscose spinning solution as defined in claim 2 wherein the modifier is a tri-ester of phosphoric acid with a polyoxyethylene glycol mono-ether of lauryl alcohol, the mono-ether containing from about 4 to 10 ethylene oxide units per mole of lauryl alcohol.

9. A viscose spinning solution as defined in claim 2 wherein the modifier is a monosodium di-ester of phosphoric acid with a polyoxyethylene glycol mono-ether of lauryl alcohol, the mono-ether containing from about 4 to 10 ethylene oxide units per mole of lauryl alcohol.

References Cited in the file of this patent UNITED STATES PATENTS 2,481,278 Ballard et al. Sept. 6, 1948 2,519,227 Collins Aug. 15, 1950 2,852,333 Cox Sept. 16,1958 

1. A VISCOSE SPINNING SOLUTION CONTAINING A SMALL AMOUNT OF A MODIFIER SELECTED FROM THE GROUP CONSISTING OF ALKALI-SOLUBLE ESTERS OF PHOSPHORIC ACID AND OF ALKALISOLUBLE ESTERS OF ALKALI-METAL ACID SALTS OF PHOSPHORIC ACID WITH POLYOXYALKYLENE GLYCOL MONO-ETHERS OF FATTY ALCOHOLS AND MIXTURES THEREOF, THE MONO-ETHERS CONTAINING AT LEAST 2 ALKYLENE OXIDE UNITS PER MOLE OF FATTY ALCOHOL, THE FATTY ALCOHOLS BEING SELECTED FROM THE GROUP CONSISTING OF SATURATED AND UNSATURATED STRAIGHT CHAIN MONOHYDRIC KYLENE OXIDE BEING SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE AND PROPYLENE OXIDE, SAID SMALL AMOUNT OF THE MODIFIER BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NON-CRENULATED SURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FORMED BY SPINNING THE VISCOSE AT A SODIUM CHLORIDE SALT TEST OF AT LEAST 7 INTO AN AQUEOUS BATH CONTAINING FROM 15% TO 22% SODIUM SULFATE, FROM 4% TO 9% ZINC SULFATE AND SULFURIC ACID IN ING 8.5%, BUT THE QUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIES OF SUCH PRODUCTS. 